This invention is a further development in sample flow cells and mixing chamber for the detection and rapid mixing of substances in a flowing stream.
Some sample flow cells in the past have had problems with light from an excitation source. See, for example, U.S. Pat. No. 4,037,974, which provides for an opaque mask and/or specially designed sample flow cell with coating material to reduce the problem of light from an excitation source. Furthermore, sampling of small flow volume has presented some difficulties with the unwanted introduction of air bubbles. See, for example, U.S. Pat. No. 4,074,940. Another problem arises in having sufficient fluorescence quantum yield for adequate detection which can be solved by a method and apparatus using a stationary phase for sampling as shown in U.S. Pat. No. 4,181,853.
Windowless flow cells by design minimize scattered light. Two previous designs for windowless spectroscopic flow cells have been reported. One design is based upon the suspension of the flowing stream between an outlet capillary tube and a small diameter rod placed directly below the outlet tube. A stationary, but constantly replenished four microliter droplet is formed in the gap between the tube and the rod. The second design is based on directing the flowing stream from a capillary tube across the gap to another capillary tube. The effluent stream is confined by sheathing with a flowing solvent to provide a windowless optical volume of 0.006 to 0.15 microliters. Diebold, G. J.; Zare, R. N., Science, 1977, 196, 1439-41 and Herschberger, L. W.; Callis, J. B.; Christian, G. D., Anal. Chem., 1979, 51, 1444-1446.